Project a plan with a deposit every month

Number of months n = term × 12 (rounded). Each month the balance is multiplied by (1 + r/12), then the monthly deposit is added (ordinary annuity: deposit after that month’s interest). Total contributed = initial + monthly × n. Estimated interest = final value − total contributed.

V_{k+1} = V_k × (1 + r/12) + m

Intérêts estimés = valeur finale − (initial + m × n)

Constant r is a teaching device. Stocks, funds, and even many “target” products vary. Deposits are end-of-month; beginning-of-month deposits would grow slightly more. Inflation, expense ratios, and tax lots are omitted. This is not an IRA contribution-limit checker.

Starting amount

Seed balance. Zero is allowed if you only contribute monthly.

Monthly contribution

Constant end-of-month add. Zero is allowed if you only have a lump sum (compound interest is then the clearer page).

Annual nominal rate

Nominal annual percent, spread as /12. 7 is 7%, not a real return after inflation.

Time

Length of the recurring-deposit plan.

Assumptions

• Fixed nominal rate, monthly compounding of the balance, end-of-month deposits.
• No withdrawals.
• n = years × 12.

Limits

• Not a Monte Carlo, not a historical backtest.
• Expense ratios and 401(k) match are not modeled unless you bake them into r and m.
• Sequence-of-returns risk is invisible in a constant r.

The final value is what a frozen 7% path would do. Treat it as a scenario, not a promise. CAGR between initial-only and the final value would ignore the deposits; this page already accounts for them in the recurrence. ROI on “final versus contributed” is a blunt ratio with no time structure — CAGR is the cleaner two-point rate if you only have endpoints.

• Adding 15 × $3,600 of deposits to a compound-interest lump-sum result by hand.

  Deposits also earn for different lengths of time. The month-by-month recurrence is the point of this page.

• Reading estimated interest as a guaranteed coupon.

  It is a residual of a constant-rate story.

• Compound interestGrow a single principal at a nominal annual rate with a chosen compounding frequency, including continuous compounding. The page also reports the effective annual rate. There are no recurring deposits on this form.
• ROIROI here is a simple ratio of gain (or loss) to cash put in. It does not know whether the outcome took a month or a decade. CAGR is the tool that uses years.
• CAGRCAGR is the fictional constant annual rate that would take a starting value to an ending value in n years. It smooths the trip: a crash and a rebound disappear into one number.
• Inflation and purchasing powerAn amount, a constant annual rate, a period. Compound forward, or bring a later sum back to today’s purchasing power.
• Simple interestInterest is proportional to principal, rate, and time. It does not itself earn interest. Use this only when a contract is actually simple, not as a stand-in for savings compounding.

Written by Rédaction HexaCalc (editorial team). Content last updated: August 25, 2026. No third-party medical or financial review is claimed.

This calculation uses a standard mathematical identity. See also the methodology.